1. Field of the Invention
The present invention relates to a control apparatus for a vehicle lamp.
2. Related Art
Conventionally, there is known an auto leveling control which automatically adjusts an optical axis position of a vehicle headlamp according to an inclination angle of a vehicle in its pitch direction to thereby change an illuminating direction of the vehicle headlamp. Generally, in the auto leveling control, as a device for detecting an inclination of the vehicle, there is used a vehicle height sensor and an optical axis position of the headlamp is adjusted according to a vehicle pitch angle detected by the vehicle height sensor. On the other hand, Patent Document 1 discloses a structure which uses a gravity sensor as an inclination detecting device. Also, Patent Document 2 discloses a structure which, as an inclination detecting device, uses a three-dimensional gyro sensor for detecting an inclination angle of the vehicle relative to a horizontal plane. Also, Patent Document 3 discloses a structure which uses, as an inclination detecting device, a clinometer for detecting a vehicle inclination angle relative to a gravitational direction. Further, Patent Document 4 discloses a structure which uses, as an inclination detecting device, an acceleration sensor for detecting the gravity acceleration of the vehicle.    Patent Document 1: JP-A-2000-085459    Patent Document 2: JP-A-2004-314856    Patent Document 3: JP-A-2001-341578    Patent Document 4: JP-A-2009-126268
When the acceleration sensor including the gravity sensor (a three-dimensional gyro sensor or the like) is used as the inclination detecting device for the vehicle, as compared with the structure using the vehicle height sensor, the auto leveling system can be produced at a lower cost and also can be reduced in weight. On the other hand, even when the acceleration sensor is used, there always exists a need to enhance a performance of the auto leveling control. One aspect of the performance of the auto leveling control is the safety of the auto leveling control. That is, the auto leveling control is required to be able to avoid a heavy degradation of a visibility of a driver even when the optical axis position is adjusted wrong by the auto leveling control.